The proportion of T lymphocytes bearing the gamma/delta and alpha/beta T cell antigen receptors was determined in histological sections of skin from normal subjects and patients suffering from acute graft-versus-host disease (GVHD) using antibodies to the delta and beta chains. The proportion of gamma/delta cells in GVHD was very low (4.3% of CD3+ cells) but significantly higher than in skin from normal donors (0.8%) and marrow recipients without GVHD (0%). The significance of this is not clear and we were unable to determine whether it represented selective localization of these cells to the skin or simply reflected peripheral blood values in the early post-transplant period in some patients with GVHD. Localization of gamma/delta cells to the epidermis was not seen; all were identified in the dermis particularly in the perivascular zone. Although it is not possible to exclude a role for gamma/delta cells in initiating GVHD, the present study suggests that they do not play an important role in producing the epidermal damage that characterizes this condition.